Many cars no come with a CD player fitted as standard but older cars may still only have a tape deck or may have a stereo that does not allow the addition of an auxiliary device or Bluetooth. With the world of technology ever evolving, more and more people are using the phones and mobile device to play music and communicate through hands-free when driving and often without Bluetooth, etc this is quite hard.
If you are looking at replacing the existing stereo in your c=vehicle to an upgraded aftermarket one, then you firstly need to find out what size it is. Some stereos are double sized and if you do buy a smaller stereo you will need to buy the correct blanking plate to fit around it.
You will often need special tools to remove the stereo from the car, these often come with the vehicle, but if not you can usually purchase them from the dealership or online from places such as Ebay and Amazon.
Once removed you often have to buy a harness and adaptor to fit the old wiring in to the new stereo. Most motor accessories companies will be able to supply you with one of these.